This invention relates to an insulated pipeline.
Pipelines for passage of oil or gas require to be insulated to prevent thermal damage to the pipe and the material passing through, and such insulation has hitherto been provided by disposing an insulating jacket, which also acts as a vapour barrier, around the pipe. Problems have arisen with such systems, however, when the insulating jacket has been continuous, since the insulating material has been insufficiently resilient to accommodate deformations in the pipe itself caused for example by low-temperature gases passing through the pipe.
To cope with this it has been proposed in West German Pat. No. 25 18940 to provide insulating material in sections spaced along the pipe, with buffer zones of resilient material between the sections to absorb pipe deformations. The insulating material lies freely on the pipe in two coaxial annular layers, of which only the outer layer is in spaced sections. The thin layer is composed of abutting sections laid end-to-end along the pipe. An outer jacket of protective material extends around the outer circumference of the insulating material.
When a pipeline is to be used in subsea environments, where hydrostatic pressure has to be encountered, for example at depths of more than 15 meters, it is necessary to provide not only heat insulation but also corrosion protection and protection against mechanical damage. In the German Patent the outer jacket provides the protection, but if it is ruptured, for example by mechanical damage, seawater should have to pass only the insulating material in order to gain access to the pipe itself. There is no particular provision for sealing the insulating layers against permeation by water, and the system described is therefore unlikely to be suitable for underwater use.
Hitherto, protection and insulation for subsea pipelines has been provided by steel sheaths having water-resistant bulkheads, but such a system is complex and bulky.